Most carpet mats are made up of two elements, one being a mat base with edges and a carpet-receiving part molded from a thermoplastic resin and the other being a needle-punched or tufted carpet bonded to the mat base with an adhesive. Carpet mats find much use as floor mats in cars, bath mats, throw rugs, etc.
In conventional carpet mat making, a mat base is first made from a resin by injection molding, press molding or casting molding, then a carpet section cut to the shape and size of the base is prepared, an adhesive is applied to one or both mating surfaces, and the base and carpet are put into registry and are bonded together. But this method is not ideal for assuring high bond strength at low cost. For instance, a car floor mat is nearly as large as one square meter and requires much adhesive to bond the mat base and carpet. Adhesive application and bonding operations are necessary after fabrication of each mat base, and the cost of the adhesive and its application accounts for the greater part of the overall cost of the carpet mat. Furthermore, this method requires a huge initial cost since it involves an applicator, dryer, conveyor and a press, as well as a work shop for application and bonding operations and a warehouse to put in mat bases before bonding operations. Applying the right amount of adhesive without fouling the edges of the mat base and bonding it to the carpet in registry requires highly skilled personnel. Most adhesives deteriorate due to heat or moisture and will not exhibit high adhesion strength over an extended period. Another factor that reduces the bonding strength of the adhesive is the uneven surface of the back side of the carpet that leaves a gap between the mating surfaces. For these reasons, the strength of the bond formed between the mat base and carpet by an adhesive is smaller than that achieved by fusion of the resin of which the mat base is made. A cross-section of the conventional mat base is shown in FIG. 1; the base consists of edges 1 which are integral with an inner carpet-receiving part 2. The edges 1 have sufficient height in order to provide good appearance, to retain the necessary strength in service and to prevent fraying, whereas the carpet-receiving part 2 is usually 1 to 2 mm thick and greater thickness is not necessary for practical purposes. The recent demand for lighter cars is another factor which necessitates the use of a thinner carpet-receiving part. FIG. 2 is a partial cross-section of a finished carpet mat, wherein the carpet 4 is bonded to the mat base through an adhesive layer 3. A cross-section of a typical injection mold unit for use in making the mat base is shown in FIG. 3; the unit consists of an upper mold 5 and a lower mold 6 with a cavity engraved in the upper mold to the size and shape of the mat base and connected to a sprue 7. A resin melted in a heating cylinder is pressed into the mold unit through the sprue 7 and fills the cavity 8. Upon cooling, the resin solidifies and can be recovered as a mat base.
For the purposes of describing the present invention in this specification, that part of the mold unit above the parting line when it is set in an injection molding machine as shown in FIG. 3 is called an "upper mold" and the part positioned below that parting line is called a "lower mold." However, these terms are not completely established in the art, and depending on the type of injection molding machines, the two molds may be positioned vertically, or the "upper mold" may be positioned under the "lower mold." With a view to developing a process for producing a carpet mat by joining a mat base to a carpet simultaneously with the making of the former by injection molding, we started by adding to the conventional mold unit of FIG. 3 a cavity made in the upper mold to accommodate a carpet. As a result of various studies that were based on this idea, we have come up with a new mold system that satisifies our object.